CYTOLOGY OF MAIZE-TRIPSACUM INTROGRESSION

The American Maydinae genera Zea and Tripsacum cross readily when not isolated from each other by gametophytic barriers, and it has been suggested that intergeneric introgression played a role in the evolution of maize. Four Zea chromosomes pair with members of at least one basic genome of tetraploid Tripsacum, and in hybrids involving octaploid Tripsacum all 10 chromosomes of the basic maize genome frequently compete successfully in synapsis with Tripsacum chromosomes. Hybrids that combine 36 Tripsacum and 10 maize chromosomes are female fertile. When they are pollinated by maize their offspring have 36 Tripsacum and 20 maize chromosomes, or again have 36 Tripsacum and 10 maize chromosomes, but the 10 Zea chromosomes are contributed by the new pollen parent. Later backcross generations also include plants with 36 Tripsacum and 12, 14, 16, or 18 maize chromosomes. Individuals with 2n = 56 produce an abundance of offspring with 18 Tripsacum and 20 maize chromosomes when backcrossed with maize. Further backcrossing results in elimination of Tripsacum chromosomes, and eventually plants with 2n = 20 Tripsacum-contaminated maize chromosomes are obtained. Two generations of selfing restore full fertility to these 2n = 20 plants and eliminate all obvious traces of Tripsacum morphology.     

Cytological and molecular characterization of oat x maize partial hybrids

In cereals, interspecific and intergeneric hybridizations (wide crosses) which yield karyotypically stable hybrid plants have been used as starting points to widen the genetic base of a crop and to construct stocks for genetic analysis. Also, uniparental genome elimination in karyotypically unstable hybrids has been utilized for cereal haploid production. We have crossed hexaploid oat (2n=6x=42, Avena sativa L.) and maize (2n=2x=20, Zea mays L.) and recovered 90 progenies through embryo rescue. Fifty-two plants (58%) produced from oatxmaize hybridization were oat haploids (2n=3x=21) following maize chromosome elimination. Twenty-eight plants (31%) were found to be stable partial hybrids with 1–4 maize chromosomes in addition to a haploid set of 21 oat chromosomes (2n=21+1 to 2n=21+4). Ten of the ninety plants produced were found to be apparent chromosomal chimeras, where some tissues in a given plant contained maize chromosomes while other tissues did not, or else different tissues contained a different number of maize chromosomes. DNA restriction fragment length polymorphisms (RFLPs) were used to identify the maize chromosome(s) present in the various oat-maize progenies. Maize chromosomes 2, 3, 4, 5, 6, 7, 8, and 9 were detected in partial hybrids and chromosomal chimeras. Maize chromosomes 1 and 10 were not detected in the plants analyzed to-date. Furthermore, partial self-fertility, which is common in oat haploids, was also observed in some oat-maize hybrids. Upon selfing, partial hybrids with one or two maize chromosomes showed nearly complete transmission of the maize chromosome to give self-fertile maize-chromosome-addition oat plants. Fertile lines were recovered that contained an added maize chromosome or chromosome pair representing six of the ten maize chromosomes. Four independently derived disomic maize chromosome addition lines contained chromosome 4, one line carried chromosome 7, two lines had chromosome 9, one had chromosome 2, and one had chromosome 3. One maize chromosome-8 monosomic addition line was also identified. We also identified a double disomic addition line containing both maize chromosomes 4 and 7. This constitutes the first report of the production of karyotypically stable partial hybrids involving highly unrelated species from two subfamilies of the Gramineae (Pooideae — oat, and Panicoideae — maize) and the subsequent recovery of fertile oat-maize chromosome addition lines. These represent novel material for gene/ marker mapping, maize chromosome manipulation, the study of maize gene expression in oat, and the transfer of maize DNA, genes, or active transposons to oat.Joint contribution of the Minnesota Agricultural Experiment Station and USDA-ARS. Scientific journal series paper No. 21 859 of the Minnesota Agricultural Experiment Station. Mention of a trademark or proprietary product does not constitute a guarantee or warranty by the USDA-ARS or the University of Minnesota and does not imply approval over other products that also may be suitable     

A comparison of apomictic reproduction in eastern gamagrass (Tripsacum dactyloides (L.) L.) and maize-Tripsacum hybrids

The expression of gene(s) governing apomictic reproduction inTripsacum provides the best foundation for comparing the effectiveness of apomictic reproduction in a series of maize-Tripsacum hybrids. Several 38-chromosome, apomictic maize-Tripsacum hybrids are available which possess the gene(s) conferring apomictic reproduction fromTripsacum. Without a base line for comparison, studies directed towards discerning the successful transfer or effectiveness of gene expression in a maize background are hampered. The objectives of this study are to compare the reproductive features found in apomicticTripsacum with those in apomictic maize-Tripsacum hybrids. In addition, this study determined the feasibility of utilizing these maize-Tripsacum hybrid materials to continue an attempt to transfer the genes into a pure maize background. The frequency and occurrence of five unique reproductive features found in apomictic accessions ofTripsacum dactyloides were compared to the reproductive behaviours exhibited in the maize-Tripsacum hybrids. Results indicate the genes controlling apomixis in tetraploidTripsacum are fully functional in maize-Tripsacum hybrids with diploid and triploid maize constitutions. The ability of theTripsacum apomictic genes to retain full expression provides evidence to continue their transfer to a diploid or tetraploid maize background.The use of company names in this publication does not imply endorsement by the USDA-ARS, or the product names or criticism of similar ones not mentioned. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap.     

Cytogenetics of double cross hybrids between Pennisetum americanum — P. purpureum amphiploids and P. americanum x Pennisetum squamulatum interspecific hybrids

Summary Pearl millet, Pennisetum americanum L. Leeke-napiergrass, Pennisetum purpureum Schum. amphiploids (2n=42) were crossed with pearl millet X Pennisetum squamulatum Fresen. interspecific hybrids (2n=41) to study the potential of germplasm transfer from wild Pennisetum species to pearl millet. These two interspecific hybrids were highly cross-compatible and more than two thousand trispecific progenies were produced from 17 double crosses. All doublecross hybrids were perennial and showed a wide range of morphological variations intermediate to both parents in vegetative and inflorescence characteristics. Some crosses resulted in sublethal progenies. Chromosomes paired mainly as bivalents (¯x15.88) or remained as univalents. At metaphase I, trivalents, quadrivalents, an occasional hexavalent and a high frequency of bivalents indicated some homeology among the genomes of the three species. Delayed separation of bivalents, unequal segregation of multivalents, lagging chromosomes, and chromatin bridges were observed at anaphase I. Although approximately 93% of the double-cross hybrids were male-sterile, pollen stainability in male-fertile plants ranged up to 94%. Seed set ranged from 0 to 37 seed per inflorescence in 71 plants under open-pollinated conditions. Apomictic embryo sac development was observed in double-cross progenies when crosses involved a pearl millet x P. squamulatum apomictic hybrid as pollen parent. These new double-cross hybrids may serve as bridging hybrids to transfer genes controlling apomixis and other plant characteristics from the wild Pennisetum species to pearl millet.     

Evolution of Ac and Dsl elements in select grasses (Poaceae)

We present data on evolution of the Ac/Ds family of transposable elements in select grasses (Poaceae). An Ac-like element was cloned from a DNA library of the grass Pennisetum glaucum (pearl millet) and 2387 bp of it have been sequenced. When the pearl millet Ac-like sequence is aligned with the corresponding region of the maize Ac sequence, it is found that all sequences corresponding to intron II in maize Ac are absent in pearl millet Ac. Kimura's evolutionary distance between maize and pearl millet Ac sequences is estimated to be 0.429±0.020 nucleotide substitutions per site. This value is not significantly different from the average number of synonymous substitutions for coding regions of the Adh1 gene between maize and pearl millet, which is 0.395±0.051 nucleotide substitutions per site. If we can assume Ac and Adh1 divergence times are equivalent between maize and pearl millet, then the above calculations suggest Ac-like sequences have probably not been strongly constrained by natural selection. The level of DNA sequence divergence between maize and pearl millet Ac sequences, the estimated date when maize and pearl millet diverged (25–40 million years ago), coupled with their reproductive isolation/lack of current genetic exchange, all support the theory that Ac-like sequences have not been recently introduced into pearl millet from maize. Instead, Ac-like sequences were probably present in the progenitor of maize and pearl millet, and have thus existed in the grasses for at least 25 million years. Ac-like sequences may be widely distributed among the grasses. We also present the first 2 Dsl controlling element sequences from teosinte species: Zea luxurians and Zea perennis. A total of 10 Dsl elements had previously been sequenced from maize and a distant maize relative, Tripsacum. When a maximum likelihood network of genetic relationships is constructed for all 12 sequenced Dsl elements, the 2 teosinte Dsl elements are as distant from most maize Dsl elements and from each other, as the maize Dsl elements are from one another. Our new teosinte sequence data support the previous conclusion that Dsl elements have been accumulating mutations independently since maize and Tripsacum diverged. We present a scenario for the origin of Dsl elements.     

Molecular analysis of crosses between Tripsacum dactyloides and Zea diploperennis (Poaceae)

 DNA fingerprinting verified hybrid plants obtained by crossing Eastern gamagrass, Tripsacum dactyloides L., and perennial teosinte, Zea diploperennis Iltis, Doebley & R. Guzmán. Pistillate inflorescences on these hybrids exhibit characteristics intermediate to the key morphological traits that differentiate domesticated maize from its wild relatives: (1) a pair of female spikelets in each cupule; (2) exposed kernels not completely covered by the cupule and outer glumes; (3) a rigid, non-shattering rachis; (4) a polystichous ear. RFLP analysis was employed to investigate the possibility that traits of domesticated maize were derived from hybridization between perennial teosinte and Tripsacum. Southern blots of restriction digested genomic DNA of parent plants, F₁, and F₂ progeny from two different crosses were probed with RFLP markers specifically associated with changes in pistillate inflorescence architecture that signal maize domestication. Pairwise analysis of restriction patterns showed traits considered missing links in the origin of maize correlate with alleles derived from Tripsacum, and the same alleles are stably inherited in second generation progeny from crosses between Tripsacum and perennial teosinte. Received: 11 October 1996/Accepted:8 November 1996     

Rapid amplification and fixation of new restriction sites in the ribosomal dna repeats in the derivatives of a cross between maize and Tripsacum dactyloides

Some of the derivatives of a cross of maize (Zea mays L.) × Tripsacum dactyloides (L) L (2n = 72) have abnormal development leading to strange and striking morphologies. The Tripsacum chromosomes in these “tripsacoid” maize plants (with Tripsacum-like characteristics) were eliminated and the maize chromosomes were recovered through repeated backcrossing to maize. As an initial attempt to analyze the DNA alterations in tripsacoid maize, we have detected a few restriction site changes in the ribosomal DNA repeat of these plants (Hpa II, Bal I, Sst I, Mbo II, and Sph I) and a new Sph I site was mapped to the spacer region between the 26S and 17S genes. Several possible mechanisms for the generation of a new restriction site are discussed, and we propose that the transient presence of Tripsacum genome during the backcrossing in some way induced a rapid amplification and fixation of new restriction sites in a relatively short period of time.     

Intergeneric hybridization between Brassica napus and Sinapis pubescens,and the cytology and crossability of their progenies

The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F₁ hybrids were dihaploid and the chromosome configurations were (0–1) _III + (2–11) _II + (5–24) _I . One F₂ plant with 38 chromosomes was obtained from open pollination of the F₁ hybrid. Thirty-one seeds were obtained from the backcross of the F₂ plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B₂ plants obtained from the backcross of B₁ plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.     

Transfer of resistance to the beet cyst nematode (Heterodera Schachtii Schm.) from Sinapis alba L. (white mustard) to the Brassica napus L. gene pool by means of sexual and somatic hybridization

Summary Sexual and somatic hybrid plants have been produced between Sinapis alba L. (white mustard) and Brassica napus L. (oil-seed rape), with the aim to transfer resistance to the beet cyst nematode Heterodera schachtii Schm. (BCN) from white mustard into the oil-seed rape gene pool. Only crosses between diploid accessions of S. alba (2n = 24, S_a1S_a1) as the pistillate parent and several B. napus accessions (2n = 38, AACC) yielded hybrid plants with 31 chromosomes. Crosses between tetraploid accessions of S. alba (2n = 48, S_a1S_a1S_a1S_a1) and B. napus were unsuccessful. Somatic hybrid plants were also obtained between a diploid accession of S. alba and B. napus. These hybrids were mitotically unstable, the number of chromosomes ranging from 56 to more than 90. Analysis of total DNA using a pea rDNA probe confirmed the hybrid nature of the sexual hybrids, whereas for the somatic hybrids a pattern identical to that of B. napus was obtained. Using chloroplast (cp) and mitochondrial (mt) DNA sequences, we found that all of the sexual F₁ hybrids and somatic hybrids contained cpDNA and mtDNA of the S. alba parent. No recombinant mtDNA or cpDNA pattern was observed. Three BC₁ plants were obtained when sexual hybrids were back-crossed with B. napus. Backcrossing of somatic hybrids with B. napus was not successful. Three sexual hybrids and one BC₁ plant, the latter obtained from a cross between a sexual hybrid and B. napus, were found to show a high level of BCN resistance. The level of BCN resistance of the somatic hybrids was in general high, but varied between cuttings from the same plant. Results from cytological studies of chromosome association at meiotic metaphase I in the sexual hybrids suggest partial homology between chromosomes of the AC and S_a1 genomes and thus their potential for gene exchange.     

In-vitro development of ovules obtained after pollination of cotton (<Emphasis Type="Italic">Gossypium</Emphasis> spp) flowers with pollen from okra (<Emphasis Type="Italic">Abelmoschus esculentus L. Moench)</Emphasis>

The in vitro response of ovules obtained after pollination of cotton flowers with pollen from Abelmoschus esculentus was studied. For this, 492 cotton flowers from five G. hirsutum varieties, four G. barbadense varieties and 10 F1 interspecific hybrids, were pollinated with pollen from A. esculentus and 5,069 ovules were cultured in vitro. From the cultured ovules, 69 embryos were isolated and 16 of them grew into plants. However, only three of them survived after transplantation. Finally, one plant which originated from the interspecific cross (B403 × Acala Sindos) × A. esculentus reached maturity. The mature plant (Pa0) had no morphological traits from A. esculentus. On the contrary, traits from both cotton species were observed. The flowcytometric analysis of the Pa0 plant indicated that it was hypoaneuploid. Root tip chromosome counts of its offsprings revealed a progressive chromosome increase from the Pa1 to Pa4 generation. Plants with 52 chromosomes or hypoaneuploids with a lower level of chromosomes (46–51) could be isolated from the Pa4 generation. These plants exhibited morphological traits from both cotton species and they were fertile. No signs of A. esculentus morphological characteristics were observed in these plants. It was concluded that aneuploid partial interspecific cotton plants could be produced after pollination of cotton interspecific hybrids with pollen from A. esculentus and application of an in-ovule embryo rescue technique.     

Composition of Esterase and Peroxidase Isoenzyme Complex, Zein-2 Protein Fraction, and SDS-Protein Complex of Zea Mays L. × Tripsacum Dactyloides L. Hybrids and Parents

The patterns of esterase and peroxidase isoenzymes, subunits of zein-2 fraction and protomers of SDS-protein complex of Zea mays L. × Tripsacum dactyloides L. hybrids and their parents were compared. The study has been made to detect specific to Tripsacum isoesterases and isoperoxidases, zein subunits and SDS-protein protomers which could be used as markers for introgression of gene loci encoding these proteins from Tripsacum into hybrids of Tripsacum with Zea mays. Isoesterases and isoperoxidases as well protomers of SDS-protein complex specific to Tripsacum were detected in all hybrids analyzed. Zein subunits, specific to Tripsacum were detected in some of the analyzed hybrids which i that introgression frequency of the loci encoding proteins studied was different. Chromosome counts taken on the examined hybrids showed the addition of 9 – 13 Tripsacum chromosomes to maize chromosome complement.     

Somatic hybrids between Solanum etuberosum and diploid,tuber bearing Solanum clones

Electrofusion was used to obtain somatic hybrids between Solanum etuberosum (2n=2x=24) and two diploid potato lines. These hybridizations were conducted to determine if haploidxwild species hybrids are better fusion partners than conventional S. tuberosumGp. Tuberosum haploids. Restriction fragment length polymerase (RFLP) analyses of the putative somatic hybrids confirmed that each parental genome was present. The somatic hybrids between S. etuberosum and a haploid S. tuberosum clone, US-W730, were stunted and had curled, purple leaves. In contrast, somatic hybrids between S. etuberosum and a haploidxwild species hybrid (US-W 730 haploidx S. berthaultii), were vigorous and generally tuberized under field conditions. These hybrids were designated as E+BT somatic hybrids. Analyses of 23 E+BT somatic hybrids revealed a statistically significant bias towards the retention of S. etuberosum chloroplasts. Stylar incompatibilities were observed when the E+BT somatic hybrids were used as pollen donors in crosses with S. tuberosum cultivars. Reciprocal crosses did not show this incompatibility. The progeny were vigorous and had improved tuber traits when compared to the maternal E+BT parent. RFLP analyses of three sexual progeny lines confirmed the presence of all 12 S. etuberosum chromosomes. In two of these lines, RFLPs that marked each of the 24 chromosome arms of S. etuberosum were present. However, RFLP markers specific for regions on chromosomes 2, 7, and 11 were missing from the third clone. Because other markers for these chromosomes were present in the progeny line, these results indicated the likelihood of pairing and recombination between S. etuberosum and S. tuberosum chromosomes.     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.     

Gamete composition and chromosome variation in pollen-derived plants from octoploid triticale x common wheat hybrids

Summary Anther culture of secondary octoploid triticale (AABBDDRR) and F₁ hybrids (AABBDDR) of octoploid triticale x common wheat crosses was carried out, and 96 pollen-derived plants were developed and studied cytologically. In addition to the 8 types of pollen-derived plants with the theoretically predicted chromosome number, plants with the chromosome constitutions of 2n = 38, 43, 45, 47, 74, and mixoploids were obtained. The haploids and the diploids had different distributions. The frequencies of plants with one and two (pairs of) rye chromosomes were extremely high, and anther culture may be an expeditious route for creating alien addition lines of distant hybrid F₁s. Chromosome aberrations, including deletions, inversions, translocations, as well as isochromosomes and ring chromosomes, were observed in some plants. Abnormal meioses, such as chromosome non-disjunction, were also found. The reasons for the chromosome aberrations are discussed.     

Primary trisomics obtained from autotriploid by diploid reciprocal crosses in cucumber

To promote cytogenetical studies on cucumber (Cucumis sativus L., 2n = 2x = 14), the reciprocal crosses were made between autotriploid and diploid for selecting the primary trisomics. Meanwhile, chromosome behavior during meiosis in autotriploid cucumber was investigated to look for cytological evidences for origin of primary trisomics. Many viable F₁ seeds were obtained from reciprocal crosses between autotriploid and diploid. The number of chromosomes of 56 surviving progenies varied from 14 to 28, with plants having 2n = 15 occurring at the highest frequency (51.8%). Primary trisomics were firstly obtained in this study. Four types of primary trisomics were isolated and they could be distinguished from each other, as well as diploid. Variable chromosome configurations, e.g. univalent, bivalents and trivalents were observed in many pollen mother cells of the autotriploid at metaphase I. Binomial chromosome distribution was observed at anaphase I and frequency of 8/13 was 6.25%. The meiosis of autotriploid, especially the class of gametes with eight chromosomes, gave the cytological evidence of producing 2x + 1 type gamete and could be induced into primary trisomic plants from progeny of autotriploid–diploid crosses. These studies have established a ground work for selecting a series of primary trisomics, and further using them for associating linkage groups with specific chromosomes in cucumber.     

Genetic studies of self-fertility in rye (Secale cereale L.). 1. The identification of genotypes of self-fertile lines for the Sf alleles of self-incompatibility genes

Segregation for self-fertility has been studied in progenies from the crosses of self-sterile (SS) plants with interline hybrids obtained by a diallel scheme of pollinations between seven self-fertile (SF) lines (nos. 2–8) and with F₁ (SS plant x SF line) hybrids. All the offspring families from the SS plant x F₁ (SS plant x SF line) crosses demonstrated a 1SF1SS segregation. The crosses of SS plants with some interline hybrids gave only self-fertile plants, whereas the crosses with other interline hybrids gave a segregation of 3SF:1SS expected in the case of digenic segregation. The data obtained permitted us to identify three different S loci (S1, S2, S5) and to estimate the genotypes of self-fertile lines for their Sf alleles: lines 5, 6, 7 and 8 are S1f/S1f S2n/S2n S5m/S5m, line 4 is S1n/S1n S2f/S2f S5m/S5m, and lines 2 and 3 are S1n/S1n S2m/S2m S5f/S5f(Sn, Sm designate active alleles of the incompatibility genes). The identification of the particular S gene which is presented by the Sf allele in each line has been made on the basis of our data concerning the linkage of the Sf mutation with isozyme markers of particular rye chromosomes, which is reported in an accompanying paper.     

OBSERVATIONS ON INTROGRESSION OF TRIPSACUM INTO MAIZE

Derivatives of a cross between diploid Zea mays L. and Tripsacum dactyloides (L.) L. (2n = 72) were compared cytologically and morphologically. The objective of this study was to detect introgression from Tripsacum to maize that might have occurred during seven backcross generations with maize. Thirty-three morphological characters were used to analyze variation among aneuploid (20Zm + 2Td), 20-chromosome recovered maize, and the recurrent maize parent plants. Aneuploid and maize checks were extreme types, with 20-chromosome hybrid derivatives being morphologically intermediate. Several recovered maizes clustered with aneuploid plants and these hybrid derivatives have the greatest chance of Tripsacum introgression. Many traits such as endosperm abnormalities, tassel seed, albinos, tunicate glumes, tassel-tipped ears, fasciated and branched ear, and male spikelets between rows of kernels were observed. Although the genetic basis of many traits is unknown, mutations, epistatic effects or expression of Tripsacum chromatin are possible causes. The number of abnormal and tripsacoid traits observed in 20-chromosome recovered maizes indicates genetic transfer from Tripsacum to the maize genome.     

Production and characterization of somatic hybrids between the Japanese radish and cauliflower

Summary Somatic hybrids between the Japanese radish and cauliflower (Brassica oleracea) were produced by protoplast electrofusion in order to introduce clubroot disease resistance in the Japanese radish (Raphanus sativus) into Brassica crops. After electrofusion of iodoacetamide-treated cauliflower protoplasts with untreated radish ones, culture was performed under conditions, that allowed only cauliflower protoplasts to regenerate. Out of 40 regenerated plants, 37 were morphologically of a hybrid type and 3 of a cauliflower type. On the basis of isozyme and RFLP analysis, all of the hybrid-type plants tested proved to be true hybrids. Of the 10 true hybrids tested, 9 were found to contain chloroplasts similar to those found in the Japanese radish, while only 1 contained those of the cauliflower. Using two mitochondrial genes as probes, we were able to show that 3 hybrids contained mitochondria of the Japanese radish, with some modification, while 7 hybrids had either parental or new patterns. All of the hybrid-type plants showed resistance to clubroot disease as high as that found in the Japanese radish. Some hybrids were self-fertile. All of the self-fertile hybrids were found to contain 36 chromosomes, indicating that they were amphidiploids. In addition, a few seeds were obtained from a backcross of the self-fertile hybrids to both parents.     

Elimination and duplication of particular Hordeum vulgare chromosomes in aneuploid interspecific Hordeum hybrids

Summary Seeds formed in crosses Hordeum lechleri (6x) x H. vulgare (2x and 4x), H. arizonicum (6x) x H. v. (2x), H. parodii (6x) x H. v. (2x), and H. tetraploidum (4x) x H. v. (2x) produced plants at high or rather high frequencies through embryo rescue. Giemsa C-banding patterns were used to analyze chromosomal constitutions and chromosomal locations on the methaphase plate. Among 100 plants obtained from H. vulgare (2x) crosses, 32 plants were aneuploid with 2n=29 (1), 28 (3), 27 (13), 26 (5), 25 (4), 24 (4), or 22 (2); 50 were euploid (12 analyzed), and 18 were polyhaploid (5 analyzed). Four plants had two sectors differing in chromosome number. Two of four hybrids with H. vulgare (4x) were euploid and two were aneuploid. Parental genomes were concentrically arranged with that of H. vulgare always found closest to the metaphase centre. Many plants showed a certain level of intraplant variation in chromosome numbers. Except for one H. vulgare (4x) hybrids, this variation was restricted to peripherally located non-H. vulgare genomes. This may reflect a less firm attachment of the chromosomes from these genomes to the spindle. Interplant variation in chromosome numbers was due to the permanent elimination or, far less common, duplication of the centrally located H. vulgare chromosomes in all 34 aneuploids, and in a few also to loss/gain of non-H, vulgare chromosomes. This selective elimination of chromosomes of the centrally located genome contrasts conditions found in diploid interspecific hybrids, which eliminate the peripherally located genome. The difference is attributed to changed genomic ratios. Derivatives of various H. vulgare lines were differently distributed among euploid hybrids, aneuploids, and polyhaploids. Chromosomal constitutions of hypoploid hybrids revealed a preferential elimination of H. vulgare chromosomes 1, 5, 6, and 7, but did not support the idea that H. vulgare chromosomes should be lost in a specific order. H. vulgare SAT-chromosomes 6 and 7 showed nucleolar dominance. Aneuploidy is ascribed to the same chromosome elimination mechanism that produces haploids in cross-combinations with H. vulgare (2x). The findings have implications for the utilization of interspecific Hordeum hybrids.     

Haploidy from Hordeum interspecific crosses

Summary Interspecific crosses of Hordeum brachyantherum (2n = 28) and H. depressum (2n = 28) with H. bulbosum (2n = 14 or 28) and H. vulgare (2n = 14 or 28) were made. Crosses between brachyantherum and diploid bulbosum resulted in dihaploids (2n = 14) of brachyantherum and hybrids (2n = 21), whilst the crosses of brachyantherum by tetraploid bulbosum or vulgare gave hybrid progeny. Similarly, crosses between H. depressum and diploid bulbosum resulted in dihaploids (2n = 14) of depressum and hybrids (2n = 21), whereas depressum by tetraploid bulbosum or vulgare invariably produced hybrids.Cytological observations on 12 day old embryos obtained from these crosses revealed chromosome variability down to 14 in crosses with diploid bulbosum indicating thereby that chromosome elimination leads to haploid formation. Embryonic cells from the brachyantherum by diploid vulgare cross also exhibited a certain degree of chromosomal instability as micronuclei.The results indicate that the ratio of parental genomes in the zygote determines whether haploids or hybrids will be produced in crosses of brachyantherum or depressum with bulbosum. Furthermore, brachyantherum appears to be more efficient in eliminating bulbosum chromosomes in comparison with depressum.